1. Field of Invention
This invention relates to pendular vibration absorbers and more particularly to fixed vibration absorbers which utilize bifilar construction and in which two dynamic masses are loaded by a spring extending therebetween and in which the natural frequency of the vibration absorber is linearized by the loads generated by the spring as the masses move relative to each other to make the absorber efficient and essentially linear throughout full pendular excursions of .+-.45.degree..
Two specially fabricated dynamic masses are each suspended by three-point or more pendular connections from a specially fabricated base member through integral pins with tapered circumferential flanges to reduce friction and damping.
The absorber may be of fixed linearized frequency or variable linearized frequency.
2. Description of the Prior Art
In the fixed vibration absorber prior art the absorbers are basically fixed frequency absorbers which are capable of absorbing vibration over a relatively small range of frequency of the principal excitation source. Typical of these absorbers are the type absorber shown in U.S. Pat. No. 3,005,520 to Mard and the battery absorber presently used in helicopters, which is basically a spring mounted weight and generally of the type disclosed in pending U.S. Patent Application Ser. No. 913,720 entitled "Tuned Spring-Mass Vibration Absorber" by John Marshall II and filed on June 7, 1978. These prior art absorbers are fixed frequency absorbers which are capable of absorbing vibrations over a relatively small range of rotor RPM. In addition, they are generally heavy, create substantial friction, and have bearings which are susceptible to wear.
Bifilar-type vibration absorbers have conventionally been used solely on rotating mechanisms, such as crankshafts of automobiles and aircraft engines and on helicopter rotors as shown in Paul and Mard U.S. Pat. No. 3,540,809. In these installations, the centrifugal force generated by rotation of the mechanism involved is necessary for the operation of the bifilar-type vibration absorber. In a fixed position vibration absorber of the type sought in this application, centrifugal force is not present. Instead, the force is generated by a spring connected within the absorber either between the masses, or between one mass and the base (latter not shown).
Another prior art absorber is shown in Desjardins et al U.S. Pat. No. 3,536,165 but it should be noted that this is not a bifilar-type vibration absorber, that it is a high friction and hence a high damping absorber and therefore a low amplification absorber so that it does not have the advantages of our bifilar-type vibration absorber.